This invention relates to a nonvolatile magnetic memory device which will simply be called a magnetic memory device or a Bloch line memory hereinafter and which memorizes information by using a pair of vertical Bloch lines in a domain wall of a stripe domain.
Magnetic memory devices of the type described are disclosed in U.S. Pat. Nos. 4,583,200 and 4,731,752 issued to Susumu Konishi et al and to Yasuharu Hidaka on April 15, 1986 and on March 15, 1988, respectively. Such a magnetic memory device uses a stripe domain which is extended along a predetermined direction in a magnetic medium, such as a ferrimagnetic garnet layer, and which has a pair of heads and an intermediate portion between the heads. The stripe domain is surrounded in the magnetic medium by a closed domain wall which has a pair of end walls and a pair of flank walls connected to the end walls.
Under the circumstances, a pair of vertical Bloch lines is written or injected as an information carrier or unit into the domain wall of the stripe domain and read out of or taken out from the stripe domain. For this purpose, the magnetic memory device comprises a write-in circuit and a readout circuit both of which are coupled to write-in and readout ends or end portions of the stripe domain in the vicinity of the heads of the stripe domain. In addition, a propagation circuit is included in the magnetic memory device so as to propagate each of the Bloch line pair from the write-in end to the readout end.
More specifically, a stripe domain is chopped by the use of the write-in circuit into a useless bubble and a remaining stripe domain into which the Bloch line pair is injected. On the other hand, the readout circuit stretches a stripe domain and also chops the stripe domain head into an information bubble and a remnant stripe domain. The information bubble conveys effective information injected into the stripe domain.
At any rate, each of the Bloch lines or each pair of the Bloch lines should be accurately located in place at the write-in and the readout ends in the predetermined direction on write-in and readout operations, respectively. To this end, an in-plane magnetic field is applied in the predetermined direction by the use of a magnetic device. However, it is very difficult to locate the Bloch line or Bloch line pair in place along the predetermined direction. This often brings about difficulty of controllability in the Bloch line or Bloch line pair and gives rise to malfunctions in the write-in and the readout operations.